The study and analysis of metal-containing anticarcinogenic compounds using chemical ionization mass spectrometry are in progress. Metal-containing compounds studied are square planar complexes of platinum, palladium, and nickel and also tetrahedral complexes of nickel. Complexes have been investigated using a variety of positive and negative reagent ions. By judicious selection of reagent ions nucleophilic and electrophilic substitution processes in the gas phase may aid in the elucidation of molecular geometry, particularly the differentiation between cis-trans isomers and complexes which can adopt either square planar or tetrahedral geometry. These results are important as an aid in determining and analyzing the metal-containing anticarcinogenic agents and in elucidating their mode of action.